1. Technical Field of the Invention
The present invention relates generally to a process and apparatus for the ultrasonic cleaning of a cylinder used in a printing press.
More particularly, the present invention provides for the ultrasonic cleaning of a printing cylinder employing rotational means for, preferably, the continuous rotation of a printing cylinder in a chamber while exposing such cylinder to sound waves having a frequency which, preferably, is in the range of 20-29 kHz for a period of time which would generally be less than 30 minutes. The means for rotation of the printing cylinder may be either magnetic or non-magnetic; the latter means being preferred. The ultrasonic cleaning of printing cylinders according to the present invention would preferably be carried out in a water-based chemical environment.
2. Description of the Prior Art
Heretofore, the removal of ink residues from engraved printing cylinders has always been a labor intensive activity which has often yielded less than acceptable results. Moreover, if the inks on the printing cylinders were not removed almost immediately from the cylinders and, instead, were allowed to dry, the cleaning of such cylinders became far more difficult, if not impossible. The complete removal of the inks was not always accomplished resulting in problems concerning the level of the quality of the print obtained when the cylinder was re-used.
In addition to the limited effectiveness of prior processes and means for cleaning printing cylinders, the typical inks which have been used by the printing industry have required a cleaning solution using a toxic, or otherwise flammable, organic solvent base. Such solvents have included, for example, acetone, methyl ethyl ketone and trichloroethane, as well as various alcohols. The health hazards to personnel working with such chemical cleaning solutions on a day-to-day basis, as well as problems of safe and legal waste disposal, are well known within the industry.
The recognized, and heretofore unfulfilled, need within the printing industry for alternative safe and effective means for the cleaning of printing cylinders has continuously grown more critical. During the past few years, safety and environmental concerns have become far more acute as the U.S. Environmental Protection Agency and OSHA, as well as various state and local agencies, have begun to strictly enforce laws and regulations governing the safe disposal and use of such potentially hazardous chemical agents.
By way of further background, one solution which has been attempted in order to overcome the foregoing health and safety concerns was the development of water-based inks as a replacement for the organically-based inks in use. Such water-based inks could, conceivably, be cleaned from the printing cylinders with cleaners having water-based solvents which could be handled and disposed of, along with the water-based inks used, in compliance with applicable health and safety requirements. When water-based inks were introduced, more and more printers began to switch to the use of such inks. This cured the problem of the safe and lawful disposal of the inks. However, it was soon realized that once the water-based inks dried on the printing cylinder and other parts of the printing presses used, they became extremely difficult to remove by conventional means.
In one sector of the trade, known as flexographic printing, the printing cylinder was coated with a ceramic. The ceramic would be coated onto the cylinder in a molten form via a process known as plasma coating. The desired printing pattern is then etched into the ceramic using a laser, with the ink cells created by the laser etching. These cells are often too small to be seen with the unaided eye. Laser etchings generally have a length, width and depth in the range of 10-40 microns. Thus, ink which had been dry within these cells became almost impossible to remove.
Cleaning methods, such as, high pressure water sprays, soaking and scrubbing with wire brushes, and the use of numerous harsh chemical agents, were all employed in various, less-than-satisfactory attempts to remove such inks. Labor costs were excessive and the result, in most cases, was a residue of dried ink in the cylinder cells causing an improper printing, and the need to shutdown the printing presses from time to time and adjust ink volumes or replace the entire printing cylinder with another. Large inventories of cylinders had to be retained in order to deal with this problem and, in many cases, printing cylinders thought to be defective were returned to suppliers for stripping, recoating and engraving at very high costs when, in actuality, such procedures were unnecessary; the printing cylinders were merely contaminated with ink trapped in the cells of the cylinders.
The use of ultrasonic energy as a procedure for cleaning a radiator having a header has been disclosed by Fields et. al. in U.S. Pat. No. 4,372,787, issued Feb. 8, 1983. Nevertheless, the potential benefits of using ultrasonic procedures in the unrelated art of cleaning printing cylinders, in order to overcome the drawbacks otherwise inherent when using organic- or water-based inks, as detained above, were never recognized by the printing industry. This was the fact that there was a widespread recognition that existing methods of effecting the cleaning of printing cylinders were time consuming, labor-intensive, not particularly effective, and often hazardous from a health and safety standpoint.